The present invention relates to a process and apparatus for measuring the cardiac capacity.
A process and an apparatus of this type have been described in U.S. Pat. No. 4,035,622.
According to the process which is the subject of the U.S. Pat. No. 4,035,622 "a quantity Q.sub.i of tracer (e.g. dye or cold liquid) is injected at constant injection flow rate D.sub.i during a time t.sub.i corresponding to at least two heart beats (two cardiac cycles), the concentration .DELTA..sub.m of tracer in the blood (or the change in blood temperature) is measured at the time t.sub.m of the end of the tracer injection and, .DELTA.(t) being the tracer concentration (or the change of temperature) as a function of time t taking t=0 at the onset of injection, one measures the integrals. ##EQU2## thus the cardiac capacity V is computed using the subsequently measured values".
But it has been established that cardiac volumes and more precise results concerning flow measurement can be obtained if some modifications are brought to the procedure by taking into account the pulsatile or non steady flow conditions of the beating heart. The modifications take into account a heart-beat by heart-beat analysis of the concentration variation and of the cardiac period .tau..sub.n ; that because the beating heart includes the cardiac valve system, the concentration variation changes in a discontinuous stepwise manner; that the period .tau..sub.n of a cardiac cycle can change over the time needed for the measurement to take place; that the washout part of the tracer curved is delayed with respect to the end of injection and takes place not at the end of injection but a little later and that subsequently not only the concentration variation has to be sampled at a given rate (e.g. 50 samples/sec) but also that the concentration level has be determined and stored at each cardiac cycle as well as the period .tau..sub.n of each of these cardiac cycles.